The invention relates to a feed apparatus for strip wrapping materials, designed for use in a wrapping machine of the type wherein the commodity to be enveloped impinges on the sheet of material.
One of the wrapping techniques most exploited, for example, in the packaging of reams of paper or of commodities in roll format, involves urging the commodity to be wrapped against a sheet of paper or plastic wrapping material, whereupon the sheet is folded around the commodity.
One design of feed apparatus for strip wrapping material, as utilized in conjunction with a machine of the type employed to implement such a technique, comprises a supply roll, a pair of pinch rolls that uncoil the strip material from the roll, cutting means such as rotating blades, accelerating means, and finally, two pairs of power driven belt loops, located on either side of the wrapping path, which grip the longitudinal edges of the sheet between their breasted surfaces. The commodity is offered to the stationary material, say, by an elevator or an actuator, at a given point along the path, whereupon the wrapping operation is effected by the machine.
A critical moment in such a process is that in which the sheet of material is brought to a halt; the sheet must in fact be stopped with considerable precision, since the material will often be printed (with script and/or images), and the writing and/or design on the wrapped commodity must appear complete and unbroken.
In current embodiments, where the material is gripped as it is engaged by the commodity, the two pairs of belts turn continuously, and use is made of pressers that pin the sheet fast, retaining it such that relative sliding motion is induced between the material and the belts.
Apparatus of this type is somewhat lacking in precision, as there is no guarantee that the sheet will stop instantly when required.
Another problem with existing feed apparatus is that of limited operating speed, the effect of which is to compromise the competitiveness of the wrapping machine as a whole.
A further, and more serious problem, however, is that of ensuring precise and sure feed of the sheet of wrapping material, also, of guaranteeing its easy withdrawal from the belts at the moment when it is separated from them by the impinging commodity.
Faultless feed of the sheet of material might be ensured through increased frictional grip, obtained by the adoption of rubber faced belts. By contrast, to ensure an easier withdrawal of the sheet from the belts (in a direction at right angles to that of the belt grip) the degree of friction must be less so as to avoid its being torn by the impinging commodity, or at all events, being damaged to the point that the packaging operation is rendered fruitless.
Accordingly, the object of the invention is that of providing a feed apparatus capable of achieving the dual purpose aforedescribed in an economical and functional manner.